1. Field of the Invention
The present invention relates to a gamma correcting circuit which is used at the time of driving panel modules, such as a liquid crystal panel and an electroluminescence panel, which needs adjustment of an applied voltage and optical characteristics.
2. Description of the Related Art
In general, the optical characteristics of panel modules, such as a liquid crystal panel and an electroluminescence panel, have a non-linear light transmission characteristic with respect to an applied voltage. This requires that the drive circuit should drive those panel modules after executing so-called gamma correcting to correct the voltage in such a way as to match with the non-linear light transmission characteristic of the panel modules.
FIG. 1 is a block diagram showing the general structure of a display system. A display panel drive apparatus 105 which drives data lines D0(1) to D0(k) of a display panel 103, includes a gamma correcting circuit 100 and a data-line drive circuit 101. A gray-scale voltage VG which has been corrected in accordance with the characteristics of the panel by the gamma correcting circuit 100 is supplied to the data-line drive circuit 101. The data-line drive circuit 101 receives gray-scale display digital data D of red, green and blue of an image, performs digital-to-analog conversion on the digital data D based on a control signal C1 from a controller 104, yielding gamma-corrected gray-scale voltages or data-line drive output voltages DO(0) to DO(k), and supplies the data-line drive output voltages DO(1) to DO(k) to the display panel 103. The scan-line drive circuit 102 drives the scan lines of the display panel 103 based on a control signal C2 from the controller 104.
FIG. 2 is a characteristic diagram showing the relationship between the gamma-corrected gray-scale display digital data and data-line drive output voltage. Generally, gamma correction is executed in accordance with the characteristics of a panel by individually changing the resistances of the gamma correcting circuit. However, there is a growing demand to facilitate the adjustment of the gamma correction characteristic by controlling gamma correction based on, for example, an adjustment signal or the like from the controller. Japanese Patent Laid-Open No. 2001-166751 discloses a gamma correcting circuit which can adjust the gamma correction characteristic.
FIG. 3 is a circuit diagram of the conventional gamma correcting circuit, disclosed in said Japanese Patent Laid-Open No. 2001-166751 (paragraphs 0037 to 0040 and FIG. 1), which can adjust the gamma correction characteristic. The gamma correcting circuit includes a reference voltage generating circuit 111, voltage adjusting circuits 112(1) to 112(n) and a gamma correction resistor circuit 113. The reference voltage generating circuit 111 generates n reference voltages by dividing a voltage by resistors provided between a high-potential power supply VH and a low-potential power supply VL. Each of the voltage adjusting circuits 112(1) to 112(n) receives an associated reference voltage, adjusts the voltage value upward or downward by causing a desired voltage drop with respect to the reference voltage based on correction adjustment data AD and outputs adjusted reference voltages V(1) to V(n). The gamma correction resistor circuit 113 outputs gray-scale voltages GV(1) to GV(8n+7) approximated to the gamma characteristic of the panel module by means of the resistors provided between the high-potential power supply VH and the low-potential power supply VL. As the outputs of the voltage adjusting circuits 112(1) to 112(n) are supplied to the output terminals for the gray-scale voltages GV(8), GV(16), . . . , and GV(8n) in the gamma correction resistor circuit 113, the correction characteristic of the gamma correction resistor circuit 113 can be adjusted by changing the gray-scale voltages GV(8), GV(16), . . . , and GV(8n) based on the correction adjustment data AD.
FIG. 4 is a characteristic diagram showing the relationship between the gamma-corrected gray-scale display digital data and data-line drive output voltage according to the prior art. As apparent from the illustration, it is possible to easily adjust the correction characteristic of the gamma correction resistor circuit 113 can be adjusted by changing the voltage values of the gray-scale voltages GV(8), GV(16), . . . , and GV(8n) based on the correction adjustment data AD and match the gamma correction characteristic with the characteristics of the panel.
However, the recent diversification of panel modules demands a highly versatile gamma correcting circuit which can adjust the gamma correction characteristic in a wider range than the prior art described in said Japanese Patent Laid-Open No. 2001-166751.